<template> 
   <ul class="list">
       <li 
            class="item" 
            v-for="item of letters" 
            :key="item"
            :ref="item"
            @touchstart.prevent= "handleTouchStart"
            @touchmove= "handleTouchMove"
            @touchend= "handleTouchEnd"
            @click="handleLetterClick"
        >{{item}}
        </li>
   </ul>
</template>


<script>
import Bscroll from 'better-scroll'
export default {
    name: 'CityAlphabet',
    props:{
        cities: Object
    },
    computed: {
        letters () {
            const letters = []
            for (let i in this.cities) {
                letters.push(i)
            }
            return letters
        }
    },
    data () {
        return {
            touchStatus: false,
            startY:0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick (e) {
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart () {
            console.log('hehe')
            this.touchStatus= true
        },
        handleTouchMove (e) {
            if(this.timer){
                clearTimeout(this.timer )
            }//函数节流
            this.timer= setTimeout(() => {
                if(this.touchStatus){
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY-this.startY)/20)
                    if(index >= 0 && index < this.letters.length){
                        this.$emit('change',this.letters[index])
                        }
                }
            }, 16);
        },
        handleTouchEnd () {
            this.touchStatus= false
        }
    }
}
</script>


<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
    .list
        display flex
        flex-direction column
        justify-content center
        position absolute
        right 0
        top 1.58rem
        bottom 0
        width .4rem
        .item
            text-align center
            line-height .4rem
            color $bgColor
</style>

